Since 2017, great white shark sightings along the Cape coastline, previously known as a hot spot for these apex predators, have become sporadic and random. The question is what has caused this? Scientist and shark experts alike have argued that its pollution, overfishing, demersal longliners bycatch, migration, and orca predation.
What is for sure is that there is a short-term disappearance after a predation by an orca on a great white shark. What’s fascinating is how do the sharks know when to leave the area?
The disappearance of great white sharks is not isolated to the Cape coastline. Salvador Jorgensen, a Senior Research Scientist, spent over 15 years studying great whites on the California coast where he tagged 165 sharks. In 2009, he noted that 17 of the 165 sharks were swimming around the Farallon Islands, when they suddenly left the area. Simultaneously, orca was spotted in the area. Not only did the sharks all flee, but they did also not return for the remainder of the season. When checking the tagged sharks, all 17 sharks were found to be alive, however, this did not rule out an attack on another shark.
Great white sharks are large predatory sharks and generally very interactive, very inquisitive and are easily seen through shark cage diving in Cape Town. So how do these animals’ sense that the orcas are nearby, to flee the area for periods of time?
To have an idea, there is need to understand the shark’s anatomy and their senses. White Sharks are shaped like torpedoes, they have 6 senses, smell, hearing, touch, taste, sight, and electromagnetism.
illustration © Alessandro De Maddalena
Smell
Sharks can smell up to 10,000 times stronger than humans. Their nostrils are located on the underside of the snout and feeds information to the olfactory bulb. The olfactory bulb is an organ which humans also use to process scents and odours. Unlike humans, the olfactory bulb is separate from the respiratory systems in sharks. Out of all the shark species, the white shark is reported to have the biggest olfactory bulb.
Hearing
Their ears are located behind their eyes, on either side of their head. They have a powerful sense of hearing and can sense the smallest vibration in the water. They have an “ear stone” which enables them to have a sense of gravity, allowing them to identify where they are in the water.
Touch
Sharks can experience touch directly and through distance. Under their skin, they have multiple nerve endings, and their teeth contain very sensitive nerves. This is why the sharks tend to bite their potential prey first to identify if the object is indeed prey or not. They also have a lateral line running from their snout to their tail. This line is made up of small pores that can pick up pressure changes in the water.
Taste
Like humans, they also have taste buds, but this is one of the poorer senses that the shark rarely uses. This because their sense of taste does not actively assist them in finding prey.
Sight
They have highly adaptable eyes that can roll backwards when attacked. Their retina has 2 areas, one used for daytime and the other for nighttime. They have a “tapetum lucidum”, which is a layer behind the retina which enables the shark to see in low light conditions as well as at night.
Finally, the sharks have an electro-reception sense, this means they can sense an electrical field. The electro receptors are in the head and snout in the form of tiny pores. These pores are highly sensitive and can pick up the faintest of electrical fields such as a muscle contraction in potential prey to the Earth’s geomagnetic field. They use the geomagnetic field to navigate the oceans during migration.
Although not much is known about how exactly the great white shark is able to vividly sense the orca, theories include smelling something in the water such as a chemical given off by the orca and shark blood after an attack, as well as detecting a stressed-out shark nearby through their electro-reception sense. As more data and research is collected, human beings will get closer to understanding how they sense these killer predators.
In the absence of the great white sharks, Apex Shark Expeditions Cape Town have been enjoying sightings of the bronze whaler shark (growing to 3.5 meters) close to Seal Island in False Bay. The trips these past months and years have been equally successful and guest feedback on cage diving in Cape Town with these other species has been outstanding.
Whales, dolphins, and many species of sea birds are often encountered on this adventurous expedition. As the business adopts an eco-system style of operating trips, going to sea with Apex is like going on a safari game drive with a promise of taking in as much marine wildlife as possible on the trips.
Book your trip today.
You might like: Whale Protects Diver From Nearby Shark
